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fla3/ops/generalized_delta_rule/dplr/wy_fast_bwd.py

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+# -*- coding: utf-8 -*-
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+
+from typing import Optional, Tuple
+
+import torch
+import triton
+import triton.language as tl
+
+from ....ops.utils import prepare_chunk_indices
+from ....utils import check_shared_mem, is_intel_alchemist, use_cuda_graph
+
+# https://github.com/intel/intel-xpu-backend-for-triton/issues/3449
+triton_config = {'grf_mode': 'large'} if is_intel_alchemist else {}
+
+
+@triton.heuristics({
+    'IS_VARLEN': lambda args: args['cu_seqlens'] is not None
+})
+@triton.autotune(
+    configs=[
+        triton.Config(triton_config, num_warps=num_warps, num_stages=num_stages)
+        for num_warps in [2, 4, 8, 16]
+        for num_stages in [2, 3, 4]
+    ],
+    key=['BT', 'BK', 'BV'],
+    use_cuda_graph=use_cuda_graph,
+)
+@triton.jit(do_not_specialize=['T'])
+def prepare_wy_repr_bwd_kernel(
+    A_ab_inv,
+    A_ak,
+    ag,
+    v,
+    dw,
+    du,
+    dv,
+    dv0,
+    dag,
+    dAak,
+    dAab,
+    cu_seqlens,
+    chunk_indices,
+    T,
+    H: tl.constexpr,
+    K: tl.constexpr,
+    V: tl.constexpr,
+    BT: tl.constexpr,
+    BK: tl.constexpr,
+    BV: tl.constexpr,
+    IS_VARLEN: tl.constexpr,
+):
+    i_t, i_bh = tl.program_id(0), tl.program_id(1)
+    i_b, i_h = i_bh // H, i_bh % H
+    if IS_VARLEN:
+        i_n, i_t = tl.load(chunk_indices + i_t * 2).to(tl.int32), tl.load(chunk_indices + i_t * 2 + 1).to(tl.int32)
+        bos, eos = tl.load(cu_seqlens + i_n).to(tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
+        T = eos - bos
+    else:
+        bos, eos = i_b * T, i_b * T + T
+
+    p_Aak_t = tl.make_block_ptr(A_ak + (bos*H + i_h) * BT,  (BT, T), (1, H*BT), (0, i_t * BT), (BT, BT), (0, 1))
+    p_Aab_inv_t = tl.make_block_ptr(A_ab_inv + (bos*H + i_h) * BT, (BT, T), (1, H*BT), (0, i_t * BT), (BT, BT), (0, 1))
+    p_dAak = tl.make_block_ptr(dAak + (bos*H + i_h) * BT, (T, BT), (H*BT, 1), (i_t * BT, 0), (BT, BT), (1, 0))
+    p_dAab = tl.make_block_ptr(dAab + (bos*H + i_h) * BT, (T, BT), (H*BT, 1), (i_t * BT, 0), (BT, BT), (1, 0))
+
+    b_A_ab_inv_t = tl.load(p_Aab_inv_t, boundary_check=(0, 1))
+    b_A_ak_t = tl.load(p_Aak_t, boundary_check=(0, 1))
+    b_A_ak_t = tl.where(tl.arange(0, BT)[:, None] < tl.arange(0, BT)[None, :], b_A_ak_t, 0)
+    b_A_ab_inv_t = tl.where(tl.arange(0, BT)[:, None] <= tl.arange(0, BT)[None, :], b_A_ab_inv_t, 0)
+    b_A_tmp_t = tl.dot(b_A_ak_t, b_A_ab_inv_t).to(v.dtype.element_ty)
+    b_dA_tmp = tl.zeros([BT, BT], dtype=tl.float32)
+
+    for i_v in range(tl.cdiv(V, BV)):
+        p_v = tl.make_block_ptr(v + (bos*H + i_h) * V, (T, V), (H*V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
+        p_dv = tl.make_block_ptr(dv + (bos*H + i_h) * V, (T, V), (H*V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
+        p_dv0 = tl.make_block_ptr(dv0 + (bos*H + i_h) * V, (T, V), (H*V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
+        p_du = tl.make_block_ptr(du + (bos*H + i_h) * V, (T, V), (H*V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
+        b_v = tl.load(p_v, boundary_check=(0, 1))
+        b_du = tl.load(p_du, boundary_check=(0, 1))
+        b_dA_tmp += tl.dot(b_du.to(b_v.dtype), tl.trans(b_v))
+        b_dv0 = tl.load(p_dv0, boundary_check=(0, 1))
+        b_dv = b_dv0 + tl.dot(b_A_tmp_t, b_du)
+        tl.store(p_dv, b_dv.to(p_dv.dtype.element_ty), boundary_check=(0, 1))
+
+    m_i = tl.arange(0, BT)[:, None] > tl.arange(0, BT)[None, :]
+    b_dA_tmp = tl.where(m_i, b_dA_tmp, 0)
+    b_dA_ak = tl.dot(b_A_ab_inv_t, b_dA_tmp)
+    b_dA_ak = tl.where(m_i, b_dA_ak, 0)
+    tl.store(p_dAak, b_dA_ak, boundary_check=(0, 1))
+    b_dA_ab_inv = tl.dot(b_dA_tmp, b_A_ak_t)
+
+    for i_k in range(tl.cdiv(K, BK)):
+        p_ag = tl.make_block_ptr(ag + (bos * H + i_h) * K, (T, K), (H*K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
+        p_dag = tl.make_block_ptr(dag + (bos * H + i_h) * K, (T, K), (H*K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
+        p_dw = tl.make_block_ptr(dw + (bos * H + i_h) * K, (T, K), (H*K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
+        b_ag = tl.load(p_ag, boundary_check=(0, 1))
+        b_dw = tl.load(p_dw, boundary_check=(0, 1))
+        b_dA_ab_inv += tl.dot(b_dw, tl.trans(b_ag))
+        b_dag = tl.dot(b_A_ab_inv_t.to(b_dw.dtype), b_dw)
+        tl.store(p_dag, b_dag.to(p_dag.dtype.element_ty), boundary_check=(0, 1))
+
+    # if we know dL/dA^(-1), for dL/dA, we can use the following formula:
+    # dL/dA = -(A^(-1))^T @ (dL/dA^(-1)) @ (A^(-1))^T
+    # in the fwd pass we use fwd substitution to calculate (I-lower(A_ab))^-1.
+    # denote A = I - lower(A_ab), B = A^-1
+    # in the backward pass.
+    # dL/dA = -(B)^T @ (dL/dB) @ B^T
+    # dL/dA_ab = lower(B^T @ dL/dB @ B^T)
+    b_dA_ab_inv = tl.where(tl.arange(0, BT)[:, None] >= tl.arange(0, BT)[None, :], b_dA_ab_inv, 0)
+    b_dA_ab_inv = tl.dot(b_A_ab_inv_t, b_dA_ab_inv)
+    b_dA_ab_inv = tl.dot(b_dA_ab_inv, b_A_ab_inv_t)
+    b_dA_ab_inv = tl.where(m_i, b_dA_ab_inv, 0)
+    tl.store(p_dAab, b_dA_ab_inv, boundary_check=(0, 1))
+
+
+def chunk_dplr_bwd_wy(
+    A_ab_inv: torch.Tensor,
+    A_ak: torch.Tensor,
+    v: torch.Tensor,
+    ag: torch.Tensor,
+    dw: torch.Tensor,
+    du: torch.Tensor,
+    dv0: torch.Tensor,
+    cu_seqlens: Optional[torch.LongTensor],
+    chunk_size: int,
+) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
+    A_ab_inv, A_ak, v, ag, dw, du = map(lambda x: x.contiguous(), [A_ab_inv, A_ak, v, ag, dw, du])
+    B, T, H, K, V = *dw.shape, du.shape[-1]
+    BT = min(chunk_size, max(triton.next_power_of_2(T), 16))
+
+    chunk_indices = prepare_chunk_indices(cu_seqlens, BT) if cu_seqlens is not None else None
+    NT = triton.cdiv(T, BT) if cu_seqlens is None else len(chunk_indices)
+    BK = min(triton.next_power_of_2(K), 64)
+    BV = min(triton.next_power_of_2(V), 64) if check_shared_mem() else min(triton.next_power_of_2(V), 32)
+
+    dA_ab = torch.empty_like(A_ab_inv, dtype=torch.float)
+    dA_ak = torch.empty_like(A_ak, dtype=torch.float)
+    dv = torch.empty_like(v)
+    dag = torch.empty_like(ag)
+
+    prepare_wy_repr_bwd_kernel[(NT, B * H)](
+        A_ab_inv=A_ab_inv,
+        A_ak=A_ak,
+        ag=ag,
+        v=v,
+        dw=dw,
+        du=du,
+        dv=dv,
+        dv0=dv0,
+        dag=dag,
+        dAak=dA_ak,
+        dAab=dA_ab,
+        cu_seqlens=cu_seqlens,
+        chunk_indices=chunk_indices,
+        T=T,
+        H=H,
+        K=K,
+        V=V,
+        BT=BT,
+        BK=BK,
+        BV=BV,
+    )
+    return dA_ab, dA_ak, dv, dag